Initdb fails on openwrt in "creating template1 database"

Hi,

I try to run postgresql on my mips based openwrt router.
Although openwrt provides precompiled packages, I have troubles
initializing postgresql's file system:

# creating template1 database in /var/postgresql/data/base/1 ...
FATAL:  could not write to file "pg_xlog/xlogtemp.1791": No space left
on device

There are about 800mb free space on /, any idea what could be the problem here?
The only strange thing I noted was, that the openwrt package was
shipped without a postgresql.conf - whereas a default configuration is
part of both, SuSE and fedora packages.

Thank you in advance, Clemens